In vivo 3D quantitative analysis of the mouse embryonic brain with a 38 MHz annular array and coded excitation

During mammalian embryogenesis the central nervous system (CNS) is the first organ to develop, and it dynamically evolves well into the postnatal stages. Magnetic resonance imaging (MRI) has traditionally been the modality of choice to visualize and analyze abnormal in vivo and fixed sample CNS phenotypes in the adult and late stage embryonic mouse. Extending these techniques for in vivo imaging of the the early stages of mouse embryo CNS will be a technical challenge for MRI with the current state of coil technology. High-frequency ultrasound imaging systems have become an important complimentary, non-invasive imaging modality which can image small structures at resolutions comparable to those of microMRI. Previous work reported on the development of a 38 MHz annular array imaging system and demonstrated its capabilities to extend the depth of field and increase the signal-to-noise ratio over traditional fixed-focus imaging transducers. Here the array system was extended by implementation of coded excitation and respiratory gating to develop an imaging protocol which has permitted the in vivo and in utero acquisition of complete volumetric datasets in about 2 minutes. After validating our protocol, we acquired volumetric datasets from 78 mouse embryos spanning embryonic days 10 to 13. The high-quality images enabled us to segment out the complete neuroanatomy of the mouse CNS and to perform statistical analysis of the CNS development.